Exploring TypeScript for the first time and grappling with the concept of generics. I'm puzzled as to why this code snippet isn't working:
function identity<T>(arg: T): T {
let num: number = 2;
return num;
}
let output = identity<number>(1);
Encountering the error: Type 'number' is not assignable to type 'T'. Shouldn't specifying the input as a number also infer that the return type should be compatible, since we've defined T as number?
When working with type T, it is important to treat it like any other existing type. Your function specifies that it expects an argument of type T and will return something of type T.
However, your code consistently returns a number, which may not necessarily be the same as T. For example, even if you call it with identity<string>("test") anticipating a string output, it would still end up being a number. This leads to a conflict in expectations.
Exploring the type signature of your identity function.
function identity<T>(arg: T)
Essentially, this function accepts an argument of type T (which is unspecified beforehand and can be anything), then returns a value of type T.
Since there is no specific information about T, the only way for the function to return a value of that type is by simply returning the provided argument. In simpler terms, there is just one possible implementation of the identity function - it returns its input.
function identity<T>(arg: T) { return arg }
The error message states:
Type 'number' is not assignable to type 'T'T is meant to be generic :)
Here is a brief narrative for you to ponder upon:
function identity<T>(arg: T): T {
let value: T = arg;
return value;
}
let result = identity<number>(1)
console.log(result);
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